Microbial cells have high potential as protein sources, being relatively cheaply grown on a wide variety of substrates, paraffins, oxygenated hydrocarbons such as alcohols, biomass, and the like. Numerous investigations and developments continue.
The natural or inherent nucleic acid content of protein from microbial cells, while high, is not objectionable for almost all animals. However, such proteins can only be used in very limited amounts by humans without reduction in nucleic acid content.
As is known, nucleic acid is metabolized by human beings but breaks down to uric acid. Uric acid is a potential problem when large amounts of nucleic acid-containing microbial cells are ingested by humans, since uric acid is far less soluble than is the normal end product of protein metabolism, urea. Buildups of uric acid may result in gout or other problems. Many patents and articles have issued describing various methods of nucleic acid reduction.
Even when the nucleic acid content is reduced to more tolerable levels, still, some human beings persistently exhibit allergic reactions to ingestion of the microbial cell derived protein.
"Allergy" simply means a hypersensitivity to a particular material, or component thereof. Many foods result in "allergy" in various people, and almost any commonly used food today results in some allergic response to at least a few individuals. And, of course, the greater the relative consumption of any single food per kilo of body weight, the greater the likelihood of allergic responses to show up within a given population.
Reduction in allergen content of microbial cell derived protein has proven particularly difficult. Since a single cell protein product frequently is intended to be consumed as an additive with other food, its presence as an additive may not be readily recognized and avoided by individuals who may be sensitive to it. Thus, it is imperative that the frequency of such allergic responses be kept low.
The adverse reactions to single cell protein materials usually fall into two broad categories, gastro-intestinal symptoms, and cutaneous symptoms. The onset of adverse symptoms may not be immediate, but may in some cases be delayed from two to as much as thirty days from the start of consumption according to Phua (M.I.T. Thesis 1981, page 11).
For single cell protein materials, it is not expected to eliminate all "allergens" to the effect that no human being will have any response at any time. What is needed, however, is a minimization of allergic responses by finding a broadly applicable method of reducing both nucleic acid and "allergens", applicable to microbial cells, and without destroying the food quality of the protein.